1. Field of the Invention
This invention relates to a process for making copolymers of maleic anhydride and an alkyl vinyl ether, and, particularly, to a solution feed solution polymerization process for making such copolymers having very low viscosities and high solids content, which are advantageous for use in non-aerosol, pump spray cosmetic products.
2. Description of the Prior Art
Several methods are known for preparing copolymers of maleic anhydride (MA) and an alkyl vinyl ether, e.g. methyl vinyl ether (MVE). For example, it is known:
(1) To react a charge of MA and a large excess of MVE in a pressure reactor. However, this method is disadvantageous because considerable heat is evolved during the polymerization, and it is difficult to remove this internally generated heat effectively. Furthermore, in the presence of a large excess of MVE, only high viscosity polymers are formed. PA1 (2) Another method involves feeding molten MA into a reactor precharged with excess MVE. However, since the MA-MVE copolymerization is a spontaneous reaction, this method generates a non-homogeneous system in which localized polymerization can occur leading to formation of homopolymers of MVE. PA1 (3) Another technique involves feeding molten MA into a reactor precharged with MVE dissolved in a solvent. This method avoids the necessity of a large excess of MVE; however, it is very difficult to monitor the feed rate of molten MA into the reactor, and, accordingly, as in process (2), localized polymerization occurs with the resultant formation of undesirable by-products. PA1 (4) In yet another method, MVE is fed into a reactor precharged with MA dissolved in a solvent. Unfortunately, this procedure does not provide very low viscosity MA-MVE copolymers having a high solids content, which properties are required for use in non-aerosol, pump spray cosmetic products.